1. Field of the Invention
This invention relates to thermosetting, low-solvent reactive polyurethane coating compositions, to a process for their production and to their use for direct, reverse and matrix reverse coating to form light-stable, non-oxidizing, non-yellowing, and non-hydrolyzing polyurethane ureas as coating polymers.
2. Description of the Prior Art
It is known that sheet-form textile materials may be coated with light-stable one-component polyurethane urea solutions containing up to 80% by weight of solvent. To obtain coating compositions of this type, which are described for example in German Offenlegungsschrift No. 2,252,280, polycarbonates containing hydroxyl groups are reacted with aliphatic diisocyanates and aliphatic diamines to form high molecular weight polyurethane ureas whose production and application involve the use of large quantities of solvents.
By contrast, low-solvent or solvent-free polyurethane coating compositions are known for example from German Offenlegungsschrift No. 2,902,090. In their case, the high molecular weight synthesis of the coating compositions is dispensed with from the outset and is replaced by the use of a suitable reactive system which may be processed in much the same way as a one-component system of the type first mentioned in conventional coating installations. The reactive components are, on the one hand, NCO-prepolymers which are produced from aromatic diisocyanates and both hydroxy polyethers and also hydroxy polyesters and of which the terminal NCO-groups are blocked with a ketoxime, and on the other hand polyamines.
Due to the presence in them of aromatic diisocyanates on the one hand and polyethers on the other hand, these coatings are not very stable to light. It is known that the subceptibility to oxidation of the above-mentioned polymer units leads to yellowing and degradation of the polymer chains and hence to a loss of tensile strength and elongation.
The same disadvantage of inadequate light stability and fastness to light also attends the chemicaly similar coating compositions according to German Offenlegungsschrift No. 2,814,079. However, since these coating compositions are primarily intended for adhesive coatings (the dispersion additive used has a thixotropic effect and prevents the coating from penetrating too deeply into the fabric), high light stability is not absolutely essential in this case either.
The object of the present invention is to provide a low-solvent reactive polyurethane urea coating system in which both the isocyanate compound and the relatively high molecular weight polyhydroxyl compound and also the amine-based crosslinking components are selected in such a way that the polymer obtained is fast to light, stable to light and, in addition, stable to oxidation and unaffected by hydrolysis. This system is intended to be readily processed--virtually as a one-component system--in conventional coating installations of the type used, for example, for PVC coatings to form dry surface coatings characterized by a high, hitherto unknown property level, the above-mentioned disadvantages of the prior art being avoided.
According to the invention, this object is achieved by the coating compositions described in detail in the following in which a special, liquid caprolactone-1,6-hexane diol polycarbonate, (cyclo)aliphatic diisocyanates and a "bis-carbazinic ester polyol" having a particularly stabilizing effect are used in a particular manner characteristic of the invention.